Deal for $699

https://www.bhphotovideo.com/c/product/1393490-REG/sigma_20mm_f_1_4_dg_hsm.html

New lens firmware

This firmware allows compatibility with Canon’s in-camera Lens Aberration Correction function to enable correction matching the optical characteristics of each lens. It also corrects the phenomenon that abnormal images appear or operation errors occur when the function is enabled. This firmware also corrects the phenomenon whereby the continuous shooting speed decreases in certain combinations with some cameras when used with the 14-24mm F2.8 DG HSM | Art for Canon, and the phenomenon whereby the AF speed occasionally becomes unstable when used with the 100-400mm F5-6.3 DG OS HSM | Contemporary for Canon.

For customers who own the SIGMA USB DOCK and applicable products listed below, please update the firmware via SIGMA Optimization Pro. Before updating the firmware using the SIGMA USB DOCK, please ensure to update SIGMA Optimization Pro to Ver. 1.4.1 or later for Windows, and Ver. 1.4.0 or later for Macintosh.

Applicable Products

• SIGMA 14mm F1.8 DG HSM | Art for CANON
• SIGMA 20mm F1.4 DG HSM | Art for CANON
• SIGMA 24mm F1.4 DG HSM | Art for CANON
• SIGMA 12-24mm F4 DG HSM | Art for CANON
• SIGMA 50-100mm F1.8 DC HSM | Art for CANON

Benefits of the Update

It has ensured compatibility with Canon’s in-camera Lens Aberration Correction function, which enables correction matching the optical characteristics of the attached lens.* It has corrected the phenomenon that abnormal images appear or operation errors occur when Canon’s in-camera Lens Aberration Correction function is enabled.

• Compatible Canon camera models:EOS-1DX mark II, EOS 5Ds, EOS 5Ds R, EOS 5D mark IV, EOS 6D mark II, EOS 80D, EOS 8000D(EOS Rebel T6s, EOS 760D), EOS 9000D(EOS 77D) , EOS Kiss x8i(EOS Rebel T6i, EOS 750D), EOS Kiss x9i(EOS Rebel T7i, EOS 800D), EOS Kiss x9(EOS Rebel SL2, EOS 200D)

https://www.sigma-global.com/jp/download/lenses/sigma-optimization-pro/

New firmware

• It becomes fully functional with the Canon Digital Cinema Camera EOS C300 Mark II.
• For SIGMA 20mm F1.4 DG HSM | Art Canon, this lens firmware update also corrects the phenomenon that the images show some underexposure when “Evaluative Metering” or “Center-weighted Average Metering” is selected on Canon EOS-1D X Mark II.

http://www.sigma-global.com/download/

I played with one of these and what impressed me most was some lights hear the edge of the image (at f1.4) were just white lights, not white in a big blob of purple. It is a kilo of glass and unstabilised (not unsurprisingly) and the coma didn't entirely grab me.

I'm also impressed at the amount of distortion. And sharp at 1.4? Sigma seems to really know what they're doing

Crops show a very good performance of this lens. At f1.4 it's very sharp in the center with some softness in the DX-corner and a hazy FX-corner that shows some coma. Compared to its longer sibling, the 24/1.4 Art, the new lens produces a sharper DX-corner and has also less coma in the FX-corner. Focus was optimized for the outer crops here but there is really only very little field-curvature. Stopping down to f2.8 produces very good sharpness and contrast across the full-frame sensor. Diffraction is clearly setting in at f11. Distortions seem pretty low for such a wide-angle lens.

http://www.cameralabs.com/reviews/Sigma_20mm_f1-4_DG_HSM_Art/

http://www.focus-numerique.com/test-2766/objectif-sigma-art-20-mm-f14-dg-hsm-flash-test-8.html

Sharpness is impressive. Even at open aperture the center is already excellent, becoming outstanding from f/2 to f4 and remaining at excellent levels right through to f/16. The edges do yield lower figures, but are still at the level of excellent all through the aperture range until it drops slightly to very good sharpness at f/16.

https://www.ephotozine.com/article/sigma-20mm-f-1-4-dg-hsm-art-review-28425

Centre sharpness remains high through from f/2 to f/11, with f/16 being adversely affected by diffraction. The edges aren't quite as sharp as the center, with f/4-f/11 producing the sharpest results.

Samples too bad to post.

http://www.photographyblog.com/reviews/sigma_20mm_f1_4_dg_hsm_review/

Sharpness is the name of the game for this 20mm version -- this lens is sharp! On a full-frame camera, even at ƒ/1.4, the Sigma 20mm ƒ/1.4 impresses with excellent center sharpness. Not surprisingly, corners display noticeable softness at ƒ/1.4, but a good portion of the frame, otherwise, remains sharp. Stopping down a bit, especially to around ƒ/2.8, really sharpens things up around the edges. The lens remains very sharp throughout the aperture range, even into the smaller apertures; however, we do see slight diffraction-related softness appear at ƒ/16.

http://slrgear.com/reviews/showproduct.php/product/1832/cat/30

I remember when sigma was the second option for a lens, a cheaper option, most of times with lower optic quality.

Today we see sigma doing the almost impossible, 18-35mm 1.8, 20mm 1.4 and so on...

When Sgima did the 20mm 1.8 I was amazed, then Nikon followed Sigma and did his better version.

I was also surprised by this 1.4 lens, but the corner performance is a little bit stretched when the background is out of focus, but not so bad, when everything is in focus the corner performance is good. Interesting thing is the amount of vignetting is small in 1.4 aperture.

I think this lens will be amazing wide open in Super35 sensors.

Hands on

http://www.dpreview.com/articles/1377431932/20-20-vision-hands-on-with-sigma-s-20mm-f1-4-art